The isolation of a lactone compound having the molecular formula C.sub.15 H.sub.18 O.sub.8 from the leaves of Ginkgo biloba was first mentioned in 1967 by R. T. Major (Science 157 (1967), 1270 to 1273). The physicochemical properties of this compound and derivatives were described, and the name bilobalid was proposed, by K. Weinges and W. Bahr (Liebigs Ann. Chem. 724 (1969), 214 to 216). The following structural formula I was proposed for bilobalid in a combined publication by the groups of K. Nakanishi et al., R. T. Major et al. and K. Weinges et al. (J. Amer. Chem. Soc. 93 (1971), 3544 to 3546) ##STR1##
No medicinal effects of bilobalid have been disclosed. However, it is known that bilobalid has no fungicidal action on Monilia fructicola and Penicillium glaucum nor any bactericidal action on Escherichia coli. Moreover, it is known that bilobalid has no inflammatory action on the mouse ear.
The known extracts prepared from Ginkgo biloba, which have been used in medicine since 1965 for the treatment of disturbances of cerebral and peripheral arterial blood flow, contain flavone glycosides as the main constituent. A typical representative of this group is 5,7,3',4'-tetrahydroxyflavono-3-O-.alpha.-rhamnopyranosyl-4-O-.beta.-D-(6" '-trans-coumaroyl)glycopyranoside of the formula II ##STR2##
These extracts, also called monoextracts (see S. S. Chatterjee and G. Trunzler, Arztezeitschrift fur Naturheilverfahren 22 (1981), 593 to 604), can, depending on the mode of their preparation, still contain small amounts of bilobalid and ginkgolides for which, however, to date no therapeutically utilisable biological actions have been disclosed.
Numerous clinical and practical reports which have been published lead to the assumption that, in addition to the therapy of disturbances of blood flow, there are favourable effects on existent neuropathies, neurological and mental functions by monoextracts prepared in a certain manner. To date, these actions have been attributed exclusively to the demonstrated actions of the monoextract in promoting blood flow. However, pharmacological investigations have shown that the monoextract possesses additional properties which go beyond the promotion of blood flow, or vascular, and which might be responsible for the improvements in nervous diseases observed clinically.